A high-quality polyacetal copolymer produced by a simple process and in an economical manner. The method includes supplying a raw material including trioxane or the like to a reaction device; obtaining a reaction mixture by carrying out a polymerization reaction of the raw material in the state where the rotating shafts are inclined by 1 to 6 upwards with respect to the horizontal direction H from the introduction opening towards a polyacetal copolymer recovery portion; vaporizing and separating an unreacted monomer from the reaction mixture using a vaporization and separation portion; re-supplying the unreacted monomer to the reaction device; and recovering the polyacetal copolymer from the reaction using a polyacetal copolymer recovery portion.

A high-quality polyacetal copolymer produced by a simple process in an economical manner. The process includes supplying a raw material including trioxane and the like to a reaction device; setting the polymerization environmental temperature to no more than 100 C. until the reaction device conversion rate becomes 0.5, and then carrying out further polymerization; vaporizing and separating unreacted monomers from the reaction mixture at an environmental temperature of at least 115 C. and less than 140 C.; supplying the separated monomers to the raw material supply; and recovering the polyacetal copolymer from the reaction mixture.

A high-quality polyacetal copolymer produced by a simple process in an economical manner. The process includes supplying a raw material including trioxane and the like to a reaction device; setting the polymerization environmental temperature to no more than 100 C. until the reaction device conversion rate becomes 0.5, and then carrying out further polymerization; vaporizing and separating unreacted monomers from the reaction mixture at an environmental temperature of at least 115 C. and less than 140 C.; supplying the separated monomers to the raw material supply; and recovering the polyacetal copolymer from the reaction mixture.

Disclosed is a technology for reducing the resistance of a secondary battery including a sulfide solid electrolyte. The secondary battery of the present disclosure includes a first electrode, an electrolyte layer, and a second electrode, wherein at least one of the first electrode and the electrolyte layer contains a sulfide solid electrolyte, and the first electrode contains a perfluoropolyether represented:

##STR00001## where Rf.sub.1 and Rf.sub.2 are each independently a C.sub.1-16 divalent alkylene group which may be substituted with one or more fluorine atoms, E.sub.1 and E.sub.2 are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C.sub.1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents, and R.sup.F is a divalent fluoropolyether group.

Disclosed is a technology for reducing the resistance of a secondary battery including a sulfide solid electrolyte. The secondary battery of the present disclosure includes a first electrode, an electrolyte layer, and a second electrode, wherein at least one of the first electrode and the electrolyte layer contains a sulfide solid electrolyte, and the first electrode contains a perfluoropolyether represented:

##STR00001## where Rf.sub.1 and Rf.sub.2 are each independently a C.sub.1-16 divalent alkylene group which may be substituted with one or more fluorine atoms, E.sub.1 and E.sub.2 are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C.sub.1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents, and R.sup.F is a divalent fluoropolyether group.